Apparatus for electrolytic polishing of rod-shaped workpieces

ABSTRACT

A tubular electrolyte container functions as a cathode and encloses a workpiece moving therethrough. The container has a cross-section corresponding to that of the workpiece. Each of a pair of seals is provided at a corresponding axial end of the container to seal the container from the workpiece and the outside. Electrolyte is continuously circulated in the container. Rollers outside the container move the workpiece through the container and supply electric current to the workpiece.

[ll] 3,720,595 H lMarch 13, 1973 United States Patent 1 Kohler 6 X X 5 2 2 0/ 424 0 "O 2 .2

Rosenquist Q t We m mm md h We S 60 577 999 ill /I/ 782 572 059 664 505 233 C I T nu ma TA CH m6 m RR F FOS S E GC mm P H A M PLO PO APW H U 3,429,798 2/1969 Beck et al............ ,...204/2()6 [75] Inventor: Ludwig Kohler,Nurnberg, Germany [73] Assignee: Siemens Aktiengesellschaft, Berlin Primary Examiner]ohn H. Mack Assistant ExaminerD. R. Valentine Attorney-Curt M. Avery, Arthur E. Wilfond, Herbert L. Lerner and Daniel J. Tick and Munich, Germany [22] Filed: June 9, 1970 [57] ABSTRACT A tubular electrolyte container functions as a cathode 21 Appl. No.: 44,720

and encloses a workpiece moving therethrough. The container has a crossth [30] Foreign Application Priority Data June 19, 1969 Germany....................

.P 19 31 174.1 section corresponding to that of e workpiece. Each of a pair of seals is provided at a corresponding axial end of the container to seal the container from the workpiece and the outside. Electrolyte is continuously circulated in the container. Rollers outside the container move the workpiece through the container and supply electric current to the workpiece.

fim u 7 7 0/32 4Mk 3 0 1 7 2 0 2 978 5 4 7 70 2 72 2 4 l i O 5 2 0-2 2 v 0 86 2n ,0 I482 4 0 l 2 5 man-D 73m "22 M N mm mm u me u "s In C lo d S Ld U .mh 1] 2 8 5v 55 [56] References Cited 8 Claims, 2 Drawing Figures UNITED STATES PATENTS 2,445,675 Lang APPARATUS FOR ELECTROLYTIC POLISHING F ROD-SHAPED WORKPIECES DESCRIPTION OF THE INVENTION paratus of the invention comprise zirconium alloys and may constitute the fuel rod sheathing tubes or the completed fuel rods of nuclear reactor installations. The fuel rod sheathing tubes must be extremely resistant to corrosion with regard to the reactor coolant which may comprise, for example, pressurized water at 300 C. This is possible, however, only when no residues at all, especially mordant residues, remain after the completion of the process of manufacture.

It has been suggested that a solution of the aforementioned problem would be to polish the zirconium components by electrolysis. Generally, the electrolytic polishing method is undertaken in a bath and the necessary electrodes are adjusted to the configuration of the workpiece. It is necessary that the current density not decrease below a minimum level. If the current density decreases below a minimum level, there would be no attainment of a smooth and shiny surface, as desired. This means that only very high currents must be utilized in the bath, in which the entire workpiece is polished by electrolysis. The high currents produce a considerable increase in the temperature of the electrolyte and also create great difficulties with regard to the supplying of said currents to the workpiece.

The principal object of the invention is to provide -new and improved apparatus for electrolytic polishing of rod-shaped workpieces.

An object of the invention is toprovide apparatus for electrolytic polishing of rod-shaped workpieces which overcomes the disadvantages of known apparatus.

An object of the invention is to provide apparatus for electrolytic polishing of rod-shaped workpieces which does not utilize high currents.

An object of the invention is to provide apparatus for electrolytic polishing of rod-shaped workpieces which does not create a considerable increase of temperature of the electrolyte.

An object of the invention is to provide apparatus for electrolytic polishing of rod-shaped workpieces, which apparatus functions with efficiency, effectiveness and reliability.

In accordance with the invention, apparatus for electrolytic polishing of rod-shaped workpieces comprising zirconium alloys moving through the apparatus comprises a tubular electrolyte container functioning as a cathode andenclosing a workpiece moving therethrough. The electrolyte container has a cross section corresponding to that of the workpiece.

Each of a pair of seals is at a corresponding axial end of the tubular electrolyte container sealing the tubular electrolyte container from the workpiece and from the outside. Duct means opening into the electrolyte container provide continuous circulation of electrolyte in the container. Roller means outside the electrolyte container in operative proximity with the workpiece move the workpiece through the electrolyte container and supply electric current to the workpiece.

The roller means comprises a pair of rollers at each axial end of the electrolyte container. One roller of each pair drives the workpiece and the other roller of each pair supplies electrical current to the workpiece. Pressurized gas is circulated adjacent the seals to maintain elasticity and proper seating of the seals. The seals comprise silicon rubber.

Each of a pair of water chambers is adjacent a corresponding one of the seals. A cooling system opening into the water chambers circulates cooling water through the water chambers thereby continuously cooling the moving workpiece as it enters and leaves the electrolyte container.

Electrolyte cooling means connected to the duct means includes cooling means and pump means for cooling and circulating electrolyte through the electreolyte container.

The electrolyte container has an inner wall having projections of substantially helical configuration thereby enlarging the interior surface of the electrolyte container and guiding the flow of the electrolyte around the workpiece in the electrolyte container. The electrolyte container comprises stainless steel. The electrolyte container comprises material having good electrical conductivity having stainless steel added thereto at the areas thereof in contact with the electrolyte.

The apparatus of the invention is of small size and permits the temperature of the electrolyte to be maintained substantially constant. This is accomplished by suitable cooling apparatus through which the electrolyte is continuously circulated. The apparatus of the invention utilizes low currents which are supplied to the workpiece via contact rollers, without difficulty. The apparatus of the invention thus provides a completely regular current distribution in the electrolyte and therefore obtains a more uniform polishing effect. In addition to the current intensity, the rate of supply of current is primarily utilized to adjust the degree of polishing. The disintegration of wall thickness, which is unavoidable in a polishing process, is very slight and amounts to approximately 0.001 to 0.01 mm.

The apparatus of the invention eliminates residues of hydrofluoric acid, which acid presented a source of damage in previously known apparatus. The residues of hydrofluoric acids are eliminated in the apparatus of the invention, since the electrolyte contains no hydrofluoride, and therefore contains no hydrofluoric residues, from any previous chemical mordants; any hydrofluorides being removed. The electrolytic residues still adhering to the surface of the workpiece are rinsed off with water. This may be accomplished in the apparatus of the invention with the cooling water which circulates through the water chambers on both sides of the sealed polishing container, around the workpieces moving through the apparatus.

In order that the invention may be readily carried into effect, it will now be described with reference to the accompanying drawing, wherein:'

FIG. 1 is a view, partly in section, of an embodiment of the apparatus of the invention for electrolytic polishing of rod-shaped workpieces; and

FIG. 2 is a view, partly in section, of part of the polishing chamber, showing a special embodiment of the electrolyte container. 7

In the FlGS., the same components are identified by the same reference numerals.

FIG. 1 is a longitudinal section through an embodiment of the apparatus of the invention for electrolytic polishing of rod-shaped workpieces. A workpiece 1, moving through the apparatus for polishing is, for example, a nuclear reactor fuel rod. A cathode 3 forms the polishing chamber for the workpiece and is sealed at one axial end by a seal 7, and at the other axial end by a seal 7. The seal 7 is provided in a body 4 of insulating material and the seal 7' is provided in a body 4 ofinsulating material. The seal 7 forms an annular cavity 13 and the seal 7 forms an annular cavity 13'.

The annular cavities 13 and 13' are filled with a pressurized gas. A counter-ring 8 is rigidly affixed to the insulating body 4 and functions as an abutment thereof. A counter-ring 8 is rigidly affixed to the insulating body 4' and functions as an abutment thereof. The annular cavities or chambers 13 and 13' are coupled to a pressurized gas line 12. The gas pressure insures that the seals 7 and 7' are always excellently seated on the workpiece 1 moving through the apparatus. The material of the seals 7 and 7' is resistant to the electrolyte. Suitable material for the seals 7 and 7' is, for example, a silicon rubber which is preferably cast in a suitable mold.

A water chamber 10 is provided adjacent the polishing chamber at one axial end thereof and is formed by the insulating body 4 and an additional insulating body 5. A water chamber 10' is provided adjacent the polishing chamber at the other axial end thereof and is formed by the insulating body 4' and an additional insulating body The water chambers and 10' are filled with cooling water or coolant via a coolant inlet 9 and coolant outlets 11 and 11'. The coolant is supplied to a recooling plant via the coolant outlets 11 and 11' from the water chambers 10 and 10', respectively, and is then resupplied to said water chambers via the coolant 9. The water chamber 10 is sealed from the outside and from the workpiece l by a simple seal 6. The water chamber 10' is sealed from the outside and from the workpiece 1 by a simple seal 6'.

The electrolyte container, which comprises the cathode 3, has an outlet 18 coupled to a cooling plant 16. The cooling plant 16 is coupled to a pump 17. The pump 17 is coupled to an inlet 19 of the electrolyte container. The cooling plant 16 cools the electrolyte and the pump 17 pumps the electrolyte back into the electrolyte container 3. The electrolyte container 3 comprises either stainless steel or copper, in order to reduce the voltage drop within the cathode. The electrolyte container 3 is plated with steel in its areas 31 and 31, in which areas it is in contact with the electrolyte.

In order to provide uniform polishing, it is preferable to provide projections of helical configuration, having a pitch 33, as shown in FIG. 2. The projections of helical configuration are provided as the inside wall of the polishing chamber or cathode 3. The projections of helical configuration thus guide the flow of electrolyte, as indicated by the arrows in FIG. 2. The flow of electrolyte is thus helically directed around the workpiece l to be polished, so that there will be no irregularities in the polishing effect, due to local heating of the electrolyte, which may otherwise possibly occur. The helically-shaped projections also assist in regulating the temperature and the cooling of the electrolyte due to their enlarged surface area.

The rod-like workpiece l is moved by a roller l5 positioned at one axial end of the apparatus, and a roller 15 positioned at the other axial end of the apparatus. A current supply roller 74 is positioned opposite the roller 15 and a current supply roller 14 is positioned opposite the roller 15'. The rollers 14 and 14' are electrically connected to the positive polarity terminal of a source of electrical current (not shown in the FIGS. in order to enhance the clarity of illustration). The workpiece l, itself, thus functions as the anode. The cathode 3 is electrically connected to the negative polarity terminal of the source of electrical current (not shown in the FIGS. in order to maintain the clarity of illustration).

It is important, for the proper operation of the apparatus, that after a workpiece 1 has moved through said apparatus, the electrolytic chamber be immediately and reliably sealed. As illustrated in FIG. 1, the immediate and reliable rescaling of the electrolytic chamber is provided by interconnecting adjacent or successive workpieces 1, la, 1b, etc., by a synthetic material member 2 having the same diameter as the workpiece. After the completion of the polishing operation and the disconnection of the current supply, the synthetic material member 2, of substantially the same shape as a workpiece, is moved into the apparatus, after the last workpiece to be polished.

The member 2 of synthetic material remains in the apparatus, thereby effectively sealing said apparatus in the same manner as an actual workpiece, until the apparatus is again operated. This prevents the electrolyte from escaping and maintains the seals 6, 6', 7 and 7 intact and in proper sealing position.

The apparatus of the invention may be utilized, for example, on zirconium alloys such as zircaloy 2 to 4, zirconium-copper alloys, steel, stainless steel, copper, and the like, when appropriate electrolytes are utilized.

The cross-section of the rod-like workpiece. 1 need not be of circular configuration. workpieces having oval, square, or other geometric cross-sectional configurations, may be polished in a similar manner. The workpieces are moved through the apparatus at a rate of approximately 1 to 10 meters per minute, when the diameter of the workpiece is 10 to 15 mm., and the current densityis 5 to amperes. The voltage is approximately ID to 50 volts.

As hereinbefore stated, a suitable electrolyte for polishing zirconium alloys is a mixture of acetic acidperchloride acid, to which hydrochloric acid and/or chloracetic acid may be added, for example. The electrolyte should be maintained at approximately room temperature, that is, between 20 to 30 C. The pressure of the pressurized gas depends upon the stiffness of the material of the seals, and is usually about I to 3 atmospheres. Usually, the desired polishing effect is provided by the removal of l to 20 microns of zirconium.

Ancillary equipment for the apparatus of the invention, necessary for its full operation, is not shown in the FIGS., in order to maintain the clarity of illustration. Thus, for example, the electrical current supply system the water cooling installations and the purifying installations are not shown in the FIGS.

The current may be supplied via the cooling water, after appropriate acidification, instead of the rollers 14 and 14'. This will increase the conductivity of the water. This is advantageous, particularly when high current densities are utilized, since it prevents a possible spark formation between the current supply rollers 14 and 14' and the workpiece 1, which would result in damage to said workpiece. The electrolyte container or cathode 3 remains the same, as do the seals 6, 6', 7 and 7, and the electrolyte flow system.

While the invention has been described by means of a specific example and in a specific embodiment, I do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

1 claim:

1. Apparatus for electrolytic polishing of rod-shaped workpieces comprising zirconium alloys moving through said apparatus, said apparatus comprising a tubular electrolyte container functioning as a cathode and adapted to enclose a workpiece movable therethrough, said electrolyte container having a crosssection corresponding to that of the workpiece; a pair of seals, each at a corresponding axial end of the tubular electrolyte container for sealing with respect to said container a workpiece passing therethrough, externally controllable pressure means for supplying pressurized gas to said seals to maintain the elasticity thereofand to seat said seals onto a workpiece passing therethrough, duct means opening into said electrolyte container for the continuous circulation of electrolyte in said container; and roller means outside said electrolyte container adapted to contact a workpiece electrically and physically for moving said workpiece through said electrolyte container and for supplying electric current to said workpiece.

2. Apparatus as claimed in claim 1, wherein said roller means comprises a pair of rollers at each axial end of said electrolyte container, one roller of each pair driving the workpiece and the other roller of each pair supplying electric current to said workpiece.

3. Apparatus as claimed in claim 1, wherein said seals comprise silicon rubber.

4. Apparatus as claimed in claim 1, further comprising a pair of water chambers each adjacent a corresponding one of said seals, and a cooling system opening into said water chambers for circulating cooling water through said water chambers thereby continuously cooling the moving workpiece as it enters and leaves said electrolyte container.

5. Apparatus as claimed in claim 1, further comprising electrolyte cooling means connected to said duct means and including cooling means and pump means for cooling and circulating electrolyte through said electrolyte container.

6. Apparatus as claimed in claim 1, wherein said electrolyte container has an inner wall having projections of substantially helical configuration thereby enlarging the interior surface of said electrolyte container and guiding the flow of the electrolyte around said workpiece in the electrolyte container.

7. Apparatus as claimed in claim 1, wherein said electrolyte container comprises stainless steel.

8. Apparatus as claimed in claim 1, wherein said electrolyte contair ler comprises material having good electrrcalconductivrty and having stainless stee a ded 

1. Apparatus for electrolytic polishing of rod-shaped workpieces comprising zirconium alloys moving through said apparatus, said apparatus comprising a tubular electrolyte container functioning as a cathode and adapted to enclose a workpiece movable therethrough, said electrolyte container having a cross-section corresponding to that of the workpiece; a pair of seals, each at a corresponding Axial end of the tubular electrolyte container for sealing with respect to said container a workpiece passing therethrough, externally controllable pressure means for supplying pressurized gas to said seals to maintain the elasticity thereof and to seat said seals onto a workpiece passing therethrough, duct means opening into said electrolyte container for the continuous circulation of electrolyte in said container; and roller means outside said electrolyte container adapted to contact a workpiece electrically and physically for moving said workpiece through said electrolyte container and for supplying electric current to said workpiece.
 2. Apparatus as claimed in claim 1, wherein said roller means comprises a pair of rollers at each axial end of said electrolyte container, one roller of each pair driving the workpiece and the other roller of each pair supplying electric current to said workpiece.
 3. Apparatus as claimed in claim 1, wherein said seals comprise silicon rubber.
 4. Apparatus as claimed in claim 1, further comprising a pair of water chambers each adjacent a corresponding one of said seals, and a cooling system opening into said water chambers for circulating cooling water through said water chambers thereby continuously cooling the moving workpiece as it enters and leaves said electrolyte container.
 5. Apparatus as claimed in claim 1, further comprising electrolyte cooling means connected to said duct means and including cooling means and pump means for cooling and circulating electrolyte through said electrolyte container.
 6. Apparatus as claimed in claim 1, wherein said electrolyte container has an inner wall having projections of substantially helical configuration thereby enlarging the interior surface of said electrolyte container and guiding the flow of the electrolyte around said workpiece in the electrolyte container.
 7. Apparatus as claimed in claim 1, wherein said electrolyte container comprises stainless steel. 